The present invention relates to a pumping system which includes a driving fluid and a driver fluid and has particular application to the pipeline transportation of solids suspended in a liquid medium to form a slurry.
The long distance pipeline transportation of such solids as coal, iron ore, sulfur, limestone and wood chips like the long distance pipeline transportation of petroleum and petroleum products offers certain advantages not common to other modes of transportation. Moreover, it is considered to be at least potentially more convenient and more economical than the more conventional means of transportation, i.e., rail or truck.
In long distance pipelining of slurries it is necessary that the pumping system employed develop a high pressure head and maintain a substantially constant velocity of slurry flow in the pipeline. In the past the most common method of transporting slurries through pipelines over long distances has involved the use of reciprocating-type pumps. However, these pumps have very high initial costs, high maintenance costs and develop substantial pulsations in the pipeline due to the non-uniform velocity of the slurry therein imparted to the slurry by the pumps. Therefore, attempts were made to employ centrifugal pumps such as used in petroleum pipelining. But such attempts proved unsuccessful where high pressure and high volume was required because the abrasive action of the slurry caused severe damage to the centrifugal pumps.
The disadvantages associated with the previous slurry pumping systems were overcome by my previous invention described in U.S. Pat. No. 3,630,638 which issued on Dec. 28, 1971, and the disclosure of which is incorporated herein by reference. This patent discloses in part a pumping system comprising one or more centrifugal pumps and a series of chambers. The chambers are adapted to be filled with a driving fluid which comprises a recirculating liquid and a driver fluid which comprises a slurry. The slurry enters the chambers at a relatively low pressure and exits at a relatively high pressure. The recirculating liquid is pressurized by the centrifugal pump or pumps and functions to apply the pressure to the slurry and this pressure forces the slurry to exit from the chambers. The two fluids, i.e., the recirculating liquid and the slurry, are separated in the chambers by movable separators which reciprocate in the chamber when the slurry enters and exits. The recirculating liquid, rather than the slurry, passes through the centrifugal pump or pumps and, because it is substantially free of any solids, abrasive action on the pump is avoided.
However, it has been found that in certain instances, i.e., when the seal between the movable separator and the chamber is worn, small amounts of the slurry may leak past the separator into the recirculating liquid. This occurs as a result of the pressure differential across the separator when a slurry entering a chamber is at a higher pressure than the recirculating liquid exiting the chamber. This leakage results in a small amount of slurry mixing with the recirculating liquid and, thus, adds solids thereto which pass through the centrifugal pumps. If this continues over an extended period of time, damage can result in the pumps.
It is therefore a primary object of this present invention to provide a pumping system having a driving fluid and a driver fluid wherein means are provided to avoid admixing of the driver fluid with the driving fluid.
These and other objects and advantages are obtained by providing in a chamber having a movable separator positioned therein, means for forcing the separator towards a first fluid on one side of the separator when a second fluid on the other side of the separator is maintained at a greater pressure than the first fluid. The means preferably pulls the separator towards the first fluid with a force which is in addition to any force caused by the pressure differential between this first and second fluids. This insures that the pressure on the side of the separator adjacent the first fluid will be greater than the pressure on the other side of the separator, thereby avoiding leakage of the second fluid past the separator into the first fluid.